Flame detection apparatus



1951 L. J. DAHLINE 2,564,597

FLAME DETECTION APPARATUS Filed Jan. 10, 1948 (Ittorneg Patented Aug. 14, 1951 FLAME DETECTION APPARATUS Lawrence J. Dahline, Minneapolis, Minn., as-

signor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application January 10, 1948, Serial No. 1,513 12 Claims. (01. 250-27) The present invention relates to an improved type of electronic flame detection apparatus of the type adapted to respond in one manner when flame is present and in another manner in the absence offlame or in the event that the flame detection circuit is not functioning properly. It is particularly related to the type of flame detector that utilizes the rectifying properties of a flame detecting device to control the operation of appropriate indicating means.

In present day applications of flame detecting apparatus to various types of burner installations, it is sometimes desirable to use a flame detector employing a" pair of flame electrodes which when positoned in the path of a flame form electrodes of a rectifier. A rectifier is formed since a flame has electrical conducting properties which, as far as the electrons in the flame are concerned, are greater in the direction of propagation of the flame. This rectifier is utilized to bias an electron discharge device which in turn operates an appropriate indicating device such as a relay to indicate the presence of flame. As the electrodes of the flame detecting device may radually become coated with the products of combustion, they tend to'act less and less as a rectifier and are apt to upset the operation of the apparatus. Further, the electrodes are generally coupled to the detecting apparatus by some appropriate shield and cable, the presence of which introduces capacity eilects into the control apparatus that may also upset the operation of the apparatus.

The present invention proposes a flame detector circuit in which the capacity of the coupling cable and the leakage resistance between the flame electrodes may be compensated for. The detecting apparatus further provides with the above provision a flame detector that will respond in a flame indicating manner only when flame is present at the flame electrodes.

It is therefore an object of the present invention to provide a flame detection apparatus which will compensate for the impedances in the flame detection circuit.

Another object of the present invention is to provide an improved flame detect-ion apparatus of the type which will be rendered operative in one sense when the flame bridges a pair of flame electrodes and in another sense when the electrodes are open circuited or short circuited.

Still another object of the present invention is to provide an improved flame detection apparatus of the type which utilizes the rectifying action of a flame bridging a pair of flame electrodes to bias an electron discharge device into and out of conduction in accordance with the presence or absence of flame across the electrodes.

A still further object of the present invention is to provide a flame detection apparatus having as a flame detection circuit a balanceable bridge by which it is possible to balance out the capacity effects on the electric circuit coupled to a pair of electrodes and the leakage resistance of the cable and the electrodes.

A still further object of the present invention is to provide a flame detection apparatus by which it is possible to determine when the flame electrodes of the flame detection circuit will require cleaning.

Other objections of the invention will be apparent from a consideration of the accompanying specification, claims and drawing in which:

The single figure represents a diagrammatic showing of my flame detection apparatus associated with a flame emitting from an oil burner.

The numeral l0 represents an oil burner of any appropriate design having a flame ll emitting from the nozzle thereof. Detecting the presence of flame is an electrode I! which is operatively connected through a shielded cable 13 to a bridge network M. The shield 68 is grounded at 69 and provides a protective covering for conductor 5|. The bridge network It may be seen to consist of an input power transformer l5 having a primary windin 16, connected to a suitable source of alternating current power, and a secondary winding IT. A pair of resistors l8 and I9 form two legs of the bridge while condensers 20 and 2| form two further legs of the bridge. Connected in parallel with the condenser 2| is a potentiometer 22. A resistor 23 is connected in series with secondary H for current limiting purposes.

An appropriate electronic indicating device is indicated by the numeral 25. The indicating device may be seen to consist of an input power transformer 26 having a primary winding 21 connected to a suitable source of power and a secondary winding 28 having a tap at 29. Operatively connected to the power transformer 26 are a pair of electron discharge devices 30 and 3|. The electron discharge device 30 is a triode tube having an anode 32, a control electrode 33, and a cathode 34. The electron discharge device 3| is also a triode tube having an anode 35, a control electrode 36 and a cathode 31. A resistor 38 is connected in biasing relation to the input of triode 30 while a pair of resistors 39 and 40 are connected in biasing relation to the input of triode 3|. A relay 4| is connected in the output circuit of the triode 3| and may be seen to consist ance of 20 megohms while the limiting resistor 23 I had a resistance of 5 megohms. Grid resistor 33 1 had a resistance of 30 megohms while the .resistors 39 and 40 had resistances of 100,000 and 15,000 ohms respectively. The voltage on the secondary winding 28 was "605) volts and was tapped at the center at tap 29. The vacuum tubes 30 and SI are preierablyincluded within a single envelope and may be of the type known coinmercially as a IZSNZ. The condenser 20 was 100 micromicrofarads and the condenser '24 was a 1-50 .microrn-icrofarad variable condenser. Potentiometer 22 had a resistance of ice megohm-s. It is to be understood these values are merely illustrative of one particular embodiment and are in nofwa y to be considered limiting-on thescope of my invention.

- Operation .In discussing the operation of the present invention; it .is important to .note that when a flame bridges a pair of flame electrodes, as occurs .in the present invention when flame Ii bridgesthe gap between burner it and the electrode 152, an electrical circuit may be completed through the flame and the conductivity of that circuit is more in one direction than in'the other. The direction of greatest electron conductivity is inlthe direction of propagation of flame, or in other words, the conventional current flow will be greatest ,in a direction opposite the direction of flame propagation. Just how this rectifying action is utilized in the subject control apparatus, .will1bc understood in the discussion that 'follows. ,In the present apparatus when flame is presentat'burner it is desirable to have relay 4! become energized so that switch blade '54 may move into engagement with its associated contact E5130 complete its electrical circuit which may be utilized in anydesirable manner-for controlling the operation or the burner or for indicating the presjenceof flame. When flame I1] is present and intersecting the electrode [2, it is possible to complete an electrical circuit from the fleft-handterminal of the secondary il through conductor 59, conductor iii of shielded cable 13, electrode I 2, flame ,l'i, burner k0, ground 52, ground '53, conductor 51%,, condenser 21, and resistor2-3 -back to the right-hand terminal of the secondary [7. Since the flame H in bridging the gap between the burner '89 and the electrode I2 forms a rectifier the alternating current from the transformer ll will be effectively rectified and the direct current component will place .a charge on condenser 25 so that it will be positive on the lower terminal .and negative on the upper terminal. The condenser 23 will also be charged so that its upper terminal is negative and its lower terminal is positive since condenser 2i; and condenser 2! are effectively connected in series opposition or in parallel in .a discharge path through the resistor 38. The electron cur rent discharge path for the charge on condenser '21 may be traced from the upper terminal o1 24 aareefiectively in parallel in the condenser 2| through conductor 55, resistor l9, conductor 51, resistor 38, conductor 58, ground 59, ground 53 and conductor t back to the lower terminal of the condenser 25. The resistor 22, which is connected in parallel with the condenser 2|. is relatively large when compared with the :resistance' of the last traced circuitso that the discharge of condenser "2i through resistor 22 has negligible effect upon the operation of the control apparatus. Since the condensers 2! and the dischage circuit through resistor 33, the electron current discharge path for condenser may be traced from the upper tei minal of the condenser through conductor Bllpre'sistor It, conductor 5?, resistor 38, conductor 58, ground 59, ground 53, conductor etiback to "the, lower terminal of condenser 20. With condensers 2i) and 2! discharging through the last traced circuits there will be a current flow through the resistor 38 such that its upper terminal will 'be negative :and its lower terrrrin'alwfll be-positive. JThiswol tage-drop from resistor 1,8 is utilized to 'bias -an electronic amplifier system in accordancelwith the current flow through the resistors.

In .theabsenceof current-flow 'throughithe re sister .38 the control electrode .33 and cathode -34 'of :the "triode '38 will be effectively operating at the same potential so thaitthe current floiw' through triode 30 will be quitellargaduringeach halfcycle when theanode is'positive'with .respectto'the cathode 3t as shown on theldiagram The circuit .for' this current Iflow may the traced from the secondary 28 at tap '29 throu h con ductor :tfl, :resistor 10, conductorltfi, anode 32, cathode es, and conductors :58, 1'58 and. 5d back to :the lower terminal of the secondary '28. With- :the large-amount of current flowing in :theila-st traced circuit there will :bea biasing voltageap plied .to the input of triodepdl sincefitis directly connected across the resistor iii! by direct connections .at the upper terminal of resistor iii] to .thecontrolelectrode 3B and apdirect connection to the lower terminal of the resistor as to the oathode .31. This biasing voltage will be such that the upper terminal of theresistor do will be negative and :a lower terminal will .be positive-so that the triode 31 will be biased to :be effectively nonconducting. The conducting .circuitfor the triode 3.! may be traced frorn theuupper terminal of the secondary 23 through conductor '55, relay winding '42, conductor 5'5, anode 35,:cathode conductors 6i and {5i back to the tap .29 or the secondary 28. .With a large amount of current flowing through the triode 35 energizing circuit the triode 3- l will'be biased below the poin'tof cur- :rent flow necessary to energize the relay M.

As soon as the condensers 12c and 21 start to discharge through the resistor 30,'such that the upper terminal of the resistor becomes negative and the "lower terminal becomes positive, the triode 30 will be biased to be eiiectively nonconducting. With the decrease in current flow in the energizing circuit for the triode '30, there will be -a decrease in the voltage drop across there- 'sistor 40 so that the triode 3| will now be biased to a potential that will permit suificient current flow to pass through the energizing circuit of triode 3| to energize relay ll. When relay ii becomes energized the switch blade M is moved into engagement with its associated switch contact 45 bythe armature 4,3 so that an electrical circuit may be completed to indicate thepresence of flame. V

*shouldthe flame H be extinguished, it-would be impossible to complete an electrical circuit will be deenergized.

In the event that there is a ground out condition, as occurs when electrode l2 shorts with burner II], it is desirable to see that the relay 4| does not become energized to indicate the presence of flame. This is accomplished in the present invention by the connection of the flame detection circuit to the bridge I4. Bridge M has as the upper two legs resistors I8 and I9 with a junction point acting as an output terminal of the bridge. The lower two legs of the bridge consist primarily of condensers 20 and 2| whose point of junction forms the other output terminal of the bridge. Connected in parallel with the condenser 20 is the flame detection circuit which may be traced from the upper terminal of condenser 20 through conductor electrode I2, flame II, burner [0, ground 52, ground 53, and conductor 55 back to the lower terminal of condenser 20. Connected in parallel with the condenser 2I is the potentiometer 22. The tap on the potentiometer 22 is normally adjusted to counterbalance the leakage resistance present in the flame detection circuit which is in parallel with the condenser 20. The condenser 2I is made variable so that the circuit capacities of the flame detection circuit in parallel with condenser 20 may be counter balanced. Thus, under normal operating conditions, the bridge I4 is balanced so that there will be no output between its output terminals at conductor 51 an ground 53. -However, in the event that the electrode I 2 should short to the burner I0 or be connected to the burner In by some low impedance shorting element, the bridge I4 will become unbalanced so that there will be an alternating current voltage on the output terminal of the bridge. Connected across the output terminals of the bridge I4 is the resistor 38 and this connection may be traced from conductor 51 through resistor 38, conductor 58, ground 59, back to the other ground terminal 53 of the bridge I 4.

As explained above, the triodes 30 and 3| form an alternating current amplier which operates on alternate half cycles of the power supply. Since it is desirable not to have relay II energized when there is a shorted condition between the electrode I2 and burner I0 it may be seen that it is desirable to have triode 3| effectively nonconducting and the triode 3|] conducting. To have triode 30 conducting it will be necessary to maintain the control electrode 33 at an effectively positive potential. This must be accomplished by the unbalance voltage of the network I4 and this unbalance voltage, since it is alternating voltage, must be phased so that the control electrode 33 is positive when the triode 30 is on its conducting half cycle. By phasing the secondary IT to be negative on its left hand terminal and positive on its right hand terminal when triode 30 is on its conducting cycle, or when secondary 28 is positive on its upper end and negative on its lower terminal as shown, the control electrode 33 will be biased by the alternating current unbalance on the bridge so that triode 30 will pass a large amount of current. With a large amount of current flowing through the triode 30 it will be impossible to energize the relay 4| since the triode 3| is effectively biased below the relay energizing point by reason of the voltage drop on the biasing resistor 40.

As it is possible to build up a shorting condition between the electrode I2 and burner ID by the continual depositing of the products of combustion on them, it is desirable to not have that shorting condition cause malfunctioning of the control apparatus. This is accomplished in the present invention by the bridge [4 with a potentiometer 22 acting in one arm thereof. As explained above, the potentiometer 22 is connected in the arm opposite the connection of the flame detection circuit so that it may be used to balance up the leakage resistance of the flame detection circuit. This balance may be accomplished by connecting any suitable voltage measuring device across the output terminals of the bridge and then adjusting the potentiometer 22 until a balance point is reached. As the leakage resistance of the flame detection circuit decreases, it will be obvious that less resistance will be required at potentiometer 22 to maintain the network balance. When the leakage resistance between the electrode l2 and the burner It] becomes too small, the direct current component of the current flowing in the flame detection circuit becomes insufl'icient to charge condensers 20 and 2| and keep them charged to bias triode 30. By calibrating the movement of the tap of potentiometer 22, it is possible to anticipate when this point is about to be reached so that the apparatus can be disassembled and the electrode I 2 on burner Il] may be cleaned.

The potentiometer 22 may also be used for a sensitivity adjustment. This may be seen when it is noted that the balance of the bridge I4 is adjustable so that if the potentiometer 22 is adjusted to unbalance the bridge in a direction to maintain 30 conducting the rectifying action of the flame detection circuit will have a greater voltage to work against in rendering triode 3B nonconducting on the presence of flame.

For various installations it may be necessary to vary the length of cable I3 which is used to connect the flame electrode I2 to the bridge network I4 which will mean the cable capacity for different installations will cause the bridge balance to be aifected by varying amounts. By making condenser 2! variable the change in the capacity of the flame detection circuit may be counterbalanced so that the bridge I4 will re main balanced.

From the foregoing it may be seen that I have provided a flame detecting apparatus which distinguishes between a flame and a short circuiting impedance in the flame detection circuit and in which it is possible to determine'the leakage impedance of a flame detection circuit and counter balance the same. It may also be seen that I have provided a flame detection apparatus where it is possible to adjust the sen-' sitivity with which the flame detection circuit will respond to the presence of flame.

Although I have described my invention in connection with an oil burner, and while it is well suited for use there, it is to be understood that it could receive application in many ways which will be obvious to those skilled in the art.

ielectrica'l circuit in parallel V :saidnetwork so that said electricalcircuit will 1 therefore intend to "be limited solely by the scopeof the appendedclaims in which I claim:

1. .A flame detection apparatus comprising in combination, a source of power, electrical signal responsive-means adapted to operate in oneman- I ner on the presence of flameand-in another man- :ner whenno flame ispresent, an :elcctrical bridge network including therein a chargeable element,

means connecting said source of power to said =responsiveimeans and said bridge network, an

electrical circuit adapted to act'as :a rectifier when bridged by a flame, means connecting-said with a :portion of -:sponsive means in accordance with the presence or absence of a flame bridging said electrical circuit.

"2. A flame detection apparatus comprising in combination, a'source of power, electrical signal responsive means adapted to operate in one'manher on the presence of flame and in another manner when no flame is present, an. electrical bridge network including therein a chargeable element, means connecting said source of power to said responsive means and said bridge network, an electrical circuit adapted to act as a rectifier when bridged by a flame, means connecting said electrical circuit in parallel with a portion or said network so that said electrical "circuit will place a charge on said chargeable element on the-presence of flame on said circuit, and means connecting said responsive means to said network so that'whensaid electrical circuit is bridged by a flame said responsive means'will be operative in said one manner and'when said electrical circuit is bridged by an impedance of 'less than a predetermined value said network will be unbalanced in a direction to maintain said responsive means operative in said other mannor.

3. A flame detection apparatus comprising in combination, a source of power, electrical signal responsive means adapted to operate in one manner on the presence of flame and in another manner when no flame is present, a 'balanceable electrical network having a chargeable element therein and having input and output terminals, means connecting said source of power to said responsive means and the input terminals of said network, an electrical circuit adapted to act as a .rectifler'when bridged by a flame, means connecting said electrical circuit in parallel with a portion of said network'so that said network will havea charge placed thereon when a flame is present at said electrical circuit and will be unbalanced when said circuit is bridged by an impedance of less than a predetermined value, and means connecting said responsive means to the output terminals of said network so that said responsive means will be operative in said one "manner when said electrical circuit is bridged by a flame and in said other manner when said circuit .is open circuited or bridged by an .impedance of less than a predetermined value.

4. A flame detection apparatus comprising in combination, a source of power, electrical signal responsive means adapted to operate in one manner on the presence of flame and in another manner when no flame is present, means connecting said source of power to said responsive means, and an electrical network adapted to render said responsive :-means operative in said one manneron the presence of flame across a portion of said network, said network comprising a balanceable electrical bridge having input and output terminals and a chargeableelement therein, means connecting said output terminals to said responsive means, means connecting said input terminals to said source of power, an-electrical circuit connected to a portionof saidbridge and adapted to act as a rectifier when bridged by a flame and to place acharge on the output terminals of said bridge, and adjustable "impedance means in a 'further portion of said bridge network for balancing the impedance added to said bridge by said-electrical circuit to prevent the impedance of said electrical circuit from rendering said responsive means operative in said other manner.

5. Aflame detection apparatus comprising combination, a source of power electrical signal responsive means adapted to operate in one manner on the presence of flame andin another -manner when no flame is present, comprising an electron discharge device, an input circuit-for said discharge device comprising, a balanceable electrical network and operable to cause-deener- .gization of said discharge device when unbalanced, an electrical circuit adapted to act as a rectifier when bridged by a flame and bias said discharge device to operate in said one-manner,

means connecting said electrical circuit toa portion of said network so that the impedance of .said circuit tends to unbalance saidnetwork,-.ad-

justable impedance means, means connecting said adjustable impedance means to a further portion of said network so that said-network will be balanced in the absence of a shorting impedance in said electrical circuit.

6. A flame detection apparatus comprising in combination, a pair of flame electrodes adapted when in an electrical circuit and bridged by a :flame to act as a rectifier, a balanceable bridge network having output terminals and comprising an adjustable impedance and a condenser, an

electrical circuit connected to said flame electrodes, means connecting said circuit in parallel with said condenser so that said condenser is charged when flame bridges said electrodes,

means connecting said adjustable impedance in counterbalancing relation to said condenser-and electricalcircuit so that said bridge is normally balanced in the absence of a shorting impedance bridging said electrodes, electrical signal responsive means adapted to operate in one manner on the presence of flame and in another manner when no flame is present, and means connecting said responsive means to the output terminals of said bridge so that said responsive means will be rendered operative in said one manner when said bridge is balanced and said condenser is charged and rendered operative in said other manner when said bridge is unbalanced,

7. A flame detection apparatus comprising incombination, a pair of flame electrodes adapted when connected in an electrical circuit and bridged bya flame toact as a rectifier, l'a'bala'nceable bridge network having output terminals and comprising a pair of condensers and a resistor, an electrical circuit connected to said flame electrodes, means connecting said circuit in parallel with one of said condensers so that said one condenser is charged when flame bridges said electrodes, means connecting the other of said condensers in counterbalancin'g relation to said one condenser and the capacity of said electrical circuit, means connecting said resistor in counterbalancing relation to the leakage resistance of said flame electrodes and said'electrical circuit so .that said bridge will be balanced in the absence of a shorting impedance'across said electrodes, electrical signal responsive means adapted to operate in one manner on the presence of flame and in another manner when no flame is present, and means connecting said responsive means to the output terminals of said bridge so that said responsive means will be rendered operative in said one manner when said bridge is balanced and said condensers are charged and rendered operative in said other manner when said bridge is unbalanced or said condensers are not charged.

8. A flame detection apparatus comprising in combination, an alternating current source of power, an electron discharge device having an anode, cathode and control electrode, means connecting the anode and cathode of said discharge device to said source of power so that said discharge device is conductive on alternate half cycles of said power supply, a balanceable bridge network having input and output terminals, a flame detection circuit adapted to act as a rectifier when bridged by a flame, a resistor, means connecting said source of power to the input terminals of said bridge, means connecting a portion of said flame detection circuit to said bridge so that said bridge will become unbalanced when said circuit is bridged by an impedance of less than a predetermined value, a condenser, means connecting said condenser as an element of said bridge so that said condenser will be charged by said flame detection circuit on the presence of flame, means connecting said resistor across the output terminals of said bridge in discharging relation to said condenser, means connecting said resistor in biasing relation to the control electrode and cathode of said discharge device so that said discharge device will be rendered operative in one range of values when said condenser is discharging through said resistor and operative in a second range of values when said condenser is not discharging or said bridge is unbalanced in a direction indicative of the presence of a shorting impedance in said flame detection circuit.

9. In combination; an electron discharge device having an anode, a cathode and a control electrode, a source of power having a plurality of points for connection, means connecting said anode to a first point on said source, means connecting said cathode to a second point on said source, a resistor, means connecting said resistor between said cathode and said control electrode, a condenser, a condition responsive impedance means which is rectifying only on the presence of a condition, means connecting said condenser in circuit with said impedance so that said condenser is charged on the presence of a condition, means connecting said resistor in discharging relation to said condenser so that when said condenser is discharging said resistor will have a voltage thereon biasing said discharge device into a first range of operation, electrical means including said condenser and said impedance means responsive to the nonrectifying impedance of said impedance means, and means connecting said electrical means to said resistor to apply a voltage thereto which will bias said discharge device into a second range of operation when the nonrectifying impedance of said im- 10 pedance means becomes less mined value.

10. In combination, an electron discharge device having an anode, a cathode and a control electrode, an alternating source of power having a plurality of points for connection, means con-' necting said anode to a first point on said source, means connecting said cathode to a second point on said source, a resistor, means connecting said resistor between said cathode and said control electrode, a condenser, a condition responsive impedance means which is rectifying only on the presence of a condition, means connecting said condenser in circuit with said impedance so that said condenser is charged on the presence of a condition, means connecting said resistor in discharging relation to said condenser so that when said condenser is discharging said resistor will have a voltage thereon biasing said discharge device into a first range of operation, electrical means having connected thereto said responsive impedance means and said condenser responsive to the nonrectifying impedance of said impedance means, and means connecting said electrical means to said resistor to apply a voltage thereto having an electrical phase which will bias said discharge device into a second range of operation when the nonrectifying impedance of said impedance means becomes less than a predetermined value.

ll. A flame detection apparatus comprising in combination; a source of power; a flame detection circuit, said circuit comprising a pair oi electrodes adapted to act as a rectifier when bridged by a flame, a condenser, and a resistor; means interconnecting said source of power, said electrodes, said resistor and said condenser in an than a predeterelectrical circuit so that said condenser is charged on the presence of a flame at said electrode and discharged through said resistor; electrical signal responsive means adapted to operate in one manner on the presence of flame and in another manner when no flame is present; means connecting said responsive means to said resistor so that said responsive means will be rendered operative in said one manner by the presence of discharge current flowing through said resistor; a balanceable network, said network including as elements thereof said flame detection circuit; and means including said network for effecting a predetermined current flow through said resistor when said electrodes are bridged by an impedance of less than a predetermined value to render said responsive means operative in said other manner.

12. A flame detection apparatus comprising in combination; a source of power; a flame detection circuit, said circuit comprising a pair of electrodes adapted to act as a rectifier when bridged by a flame, a condenser, and a resistor; means interconnecting said source of power, said electrodes, said resistor and said condenser in an electrical circuit so that said condenser is charged on the presence of flame at said electrodes and discharged through said resistor; an electron discharge device having an anode, cathode and control electrode; electrical signal responsive means; means connecting said responsive means in operational responsive relation in the anode circuit of said discharge device; means connecting said resistor between the cathode and control electrode of said discharge device so that said discharge device will be operative in one range only when said resistor has discharging currents flowing therethrough; a balanceable network,

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